Three different versions of the underdetermination thesis are identified in the later writings of the Edinburgh School by which its relativism is maintained. These I call the Stratagems UT, the Floating-feather UT, and the Oxygen UT. It is argued the marshalling of historiographical evidence to support the Floating-feather UT involves a version of the Liar’s paradox; that a variant of the Stratagems UT with the evidence provided by the Edinburgh School is internally inconsistent; that the Edinburgh School has failed to show the adequacy and the conformity of the historical evidence offered to support the Oxygen UT; that the Oxygen UT thoroughly neutralizes empirical evidence of any efficacy, and, thus, of any role, first, in the truth/falsity evaluation of the theory at the physical level, and second, in the explanation of theory-evaluation at the explanatory metaphysical or socio-historical level. I also show that Larry Laudan is quite mistaken in concurring with the Edinburgh School’s thesis of symmetrical explanation of theories insofar as their epistemic status is concerned.